In airplanes driven by an internal combustion engine, gasoline engines, diesel engines or two-cycle engines mostly are used. In certain flight phases, these internal combustion engines are operated with increased power. The excess power produced thereby is required for instance during take-off of the aircraft or in the safety-critical climbing phase subsequent to take-off. The internal combustion engine, however, is operated with a particularly high rotational speed and load, whereby wear is increased superproportionally.
In addition, airplanes are known, which are driven exclusively by an electric motor. DE 195 12 816 A1 proposes a glider with auxiliary motor which constitutes an electric motor, wherein the energy supply of the electric motor is ensured by a battery means arranged in the wings.
When a conventional airplane with an internal combustion engine requires an increased drive power, it has been necessary so far to use an internal combustion engine of greater power. The resulting increase in weight, however, has led to higher requirements of the aircraft structure and hence to an increased total weight.
Therefore, it is the problem underlying the invention to provide an aircraft which can provide an increased drive power, without the mass of the drive being significantly increased thereby.
For the solution of this object in accordance with the invention, it is provided in an aircraft as mentioned above that the internal combustion engine cooperates with an electric machine, which in a first operating mode is operable as electric motor and in a second operating mode as electric generator.
This invention is based on the knowledge that the electric motor can be combined with the electric machine to form a hybrid motor, in order to support the internal combustion engine and provide an increased drive power in certain operating conditions. Primarily, the electric machine merely is used during short flight phases, for instance during take-off or in climbing flight, and then supplies a safety-relevant excess of power. It is preferred that the additional drive power amounts to about 15% to 35%, preferably 20%, of the power of the internal combustion engine. However, the mass increase caused by the electric machine and possibly required further components lies distinctly below the mass increase during use of a more powerful internal combustion engine. When the additional power no longer is required, the electric machine is switched off or switched into the second operating mode and then acts as an electric generator. The electric machine is connected with at least one accumulator as energy storage device, which provides the energy required during operation as electric motor and can be charged in the second operating mode during operation as generator. Upon termination of the charging operation, the additional drive power can be retrieved again. This provides the advantage that in cruising flight the internal combustion engine is loaded more efficiently, whereby the fuel consumption is reduced due to a more favorable design of the internal combustion engine.
Preferably, the aircraft of the invention includes two or more accumulators which are arranged in the wings. This provides a more favorable mass distribution of the aircraft, so that the aircraft structure can be designed lighter in weight, which in turn leads to a reduced power demand and a reduced fuel consumption.
In the aircraft of the invention, another advantage is obtained when the at least one accumulator provides the energy for the on-board power supply of the aircraft. In this case, a separate accumulator can be omitted, whereby the mass of the aircraft is further reduced.
In accordance with a development of the invention it can be provided that the electric machine is designed for starting the internal combustion engine. The electric machine then serves as starter generator, so that a separate electric motor as starter can be omitted, whereby a further reduction of the mass of the drive is obtained.
In the aircraft of the invention, the electric machine can be connected with the crankshaft of the internal combustion engine rigidly or via a clutch. When a clutch is present, the electric machine particularly advantageously only is connected with the internal combustion engine when required, i.e. when the electric machine is operated as electric motor and provides the increased power, or alternatively when the electric machine is operated as generator and charges the accumulator. In all other flight conditions, the electric machine can be coupled out, so that it does not exert a load on the internal combustion engine. Configurations are conceivable, however, in which the electric machine is rigidly connected with the crankshaft of the internal combustion engine. The electric machine acts as an additional centrifugal mass, which with a suitable design leads to a smoother run of the internal combustion engine. Accordingly, additional centrifugal masses as used in conventional internal combustion engines can be omitted.
In accordance with a first aspect of the invention it can be provided that the electric machine is arranged at the end of the crankshaft opposite to the propeller. In accordance with an alternative aspect, it can, however, also be provided that the electric machine is arranged on the crankshaft between propeller and internal combustion engine. Possibly, the electric machine can be coupled or capable of being coupled to the crankshaft via a propeller transmission or a separate transmission or via a belt drive.
It is particularly preferred that the aircraft of the invention includes a control unit which controls a carburetor or an injection system of the internal combustion engine and a charging and power electronics for the electric machine. With the power electronics, the actuation of the electric machine is accomplished during operation as electric motor. The charging electronics additionally can include a device for monitoring the condition of the accumulator.
A particularly simple operation of the aircraft of the invention is obtained when the control unit is operable by a control element preferably constituting a single-lever control. The pilot merely operates a power lever in a conventional way, whereas the control of the electric machine, in particular switching on or off the first operating mode as electric motor and switching on and off the second operating mode as generator is performed automatically by the control unit, in particular in dependence on the position of the control element, preferably of the power lever. Control and switching are effected automatically and hence without action of the pilot, whereby operating errors are excluded.
The invention can be used in all aircrafts driven by an internal combustion engine, in particular in motor airplanes, ultralight aircrafts, trikes, motor gliders and gliders with auxiliary engine. In addition, it is also suitable for those aircrafts which are permitted as Light Sport Aircraft (LSA) or Very Light Aircraft (VLA).